The equator and all meridians are great circles.)Ībove and below the equator, the circles defining the parallels of latitude get gradually smaller until they become a single point at the North and South Poles where the meridians converge. (Circles with the same radius as the spherical earth are called great circles. This is because the equator is the only parallel as large as a meridian. Only along the equator does the distance represented by one degree of longitude approximate the distance represented by one degree of latitude.
CHANGE COORDINATE SYSTEM ARCGIS PLUS
For example, the location of Los Angeles, California, is roughly plus 33 degrees, 56 minutes latitude and minus 118 degrees, 24 minutes longitude.Īlthough longitude and latitude can locate exact positions on the surface of the globe, they do not provide uniform units of measure for length and distance. West of the prime meridian is typically recorded as negative longitude, and east is recorded as positive. Longitude measures are traditionally based on the prime meridian, which is an imaginary line running from the North Pole through Greenwich, England, to the South Pole. Longitude measures angles in an east–west direction. This type of coordinate reference system is often referred to as a geographic coordinate system. They are measures of the angles (in degrees) from the center of the earth to a point on the earth's surface. One method for describing the position of a geographic location on the earth's surface is using spherical measures of latitude and longitude. In this way, multiple GIS data layers can be overlaid onto the earth's surface. GIS datasets contain coordinate locations within a global or Cartesian coordinate system to record geographic locations and shapes. The geographic elements contained in various map layers are drawn in a specific order (one on top of another) for the given map extent. Maps represent locations on the earth's surface using grids, graticules, and tic marks labeled with various ground locations-both in measures of latitude-longitude and in projected coordinate systems such as UTM meters.
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Another is a planar or Cartesian coordinate system derived from the global framework. A global coordinate system of latitude-longitude is one such framework. A geographic coordinate system is used to assign geographic locations to objects. The ability to accurately locate geographic features is critical in both mapping and GIS.ĭescribing the correct location and shape of features requires a coordinate framework for defining real-world locations.
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All the elements in a map layer have a specific geographic location and extent that enables them to be located on or near the earth's surface. Georeferencing is about using map coordinates to assign a spatial location to map features.